479 research outputs found
Thermodynamically stable lithium silicides and germanides from density-functional theory calculations
Density-functional-theory (DFT) calculations have been performed on the Li-Si
and Li-Ge systems. Lithiated Si and Ge, including their metastable phases, play
an important technological r\^ole as Li-ion battery (LIB) anodes. The
calculations comprise structural optimisations on crystal structures obtained
by swapping atomic species to Li-Si and Li-Ge from the X-Y structures in the
International Crystal Structure Database, where X={Li,Na,K,Rb,Cs} and
Y={Si,Ge,Sn,Pb}. To complement this at various Li-Si and Li-Ge stoichiometries,
ab initio random structure searching (AIRSS) was also performed. Between the
ground-state stoichiometries, including the recently found LiSi
phase, the average voltages were calculated, indicating that germanium may be a
safer alternative to silicon anodes in LIB, due to its higher lithium insertion
voltage. Calculations predict high-density LiSi and LiGe
layered phases which become the ground state above 2.5 and 5 GPa
respectively and reveal silicon and germanium's propensity to form dumbbells in
the LiSi, stoichiometry range. DFT predicts the stability of
the LiGe , LiGe and LiGe
phases and several new Li-Ge compounds, with stoichiometries LiGe,
LiGe, LiGe and LiGe.Comment: 10 pages, 5 figure
Time Evolution and Deterministic Optimisation of Correlator Product States
We study a restricted class of correlator product states (CPS) for a
spin-half chain in which each spin is contained in just two overlapping
plaquettes. This class is also a restriction upon matrix product states (MPS)
with local dimension ( being the size of the overlapping regions of
plaquettes) equal to the bond dimension. We investigate the trade-off between
gains in efficiency due to this restriction against losses in fidelity. The
time-dependent variational principle formulated for these states is numerically
very stable. Moreover, it shows significant gains in efficiency compared to the
naively related matrix product states - the evolution or optimisation scales as
for the correlator product states versus for the unrestricted
matrix product state. However, much of this advantage is offset by a
significant reduction in fidelity. Correlator product states break the local
Hilbert space symmetry by the explicit selection of a local basis. We
investigate this dependence in detail and formulate the broad principles under
which correlator product states may be a useful tool. In particular, we find
that scaling with overlap/bond order may be more stable with correlator product
states allowing a more efficient extraction of critical exponents - we present
an example in which the use of correlator product states is several orders of
magnitude quicker than matrix product states.Comment: 19 pages, 14 figure
F17RS SGR No. 17 (Coaxial Cables)
A RESOLUTION
To urge and request the Residence Hall Association (RHA) to provide coaxial cables for residents living in the Residence Hall
Reporting of conflicts of interest in oral presentations at medical conferences : a delegate-based prospective observational study
Β© Article author(s) (or their employer(s) unless otherwise stated in the text of the article) 2017. All rights reserved. No commercial use is permitted unless otherwise expressly granted.Peer reviewedPublisher PD
Energetics of hydrogen/lithium complexes in silicon analyzed using the Maxwell construction
We have studied hydrogen/lithium complexes in crystalline silicon using
density-functional-theory methods and the ab initio random structure searching
(AIRSS) method for predicting structures. A method based on the Maxwell
construction and convex hull diagrams is introduced which gives a graphical
representation of the relative stabilities of point defects in a crystal and
enables visualization of the changes in stability when the chemical potentials
are altered. We have used this approach to study lithium and hydrogen
impurities in silicon, which models aspects of the anode material in the
recently-suggested lithium-ion batteries. We show that hydrogen may play a role
in these anodes, finding that hydrogen atoms bind to three-atom lithium
clusters in silicon, forming stable {H,3Li} and {2H,3Li} complexes, while the
{H,2Li} complex is almost stable.Comment: (5 pages, 4 figures
Calcium supplements with or without vitamin D and risk of cardiovascular events : reanalysis of the Women's Health Initiative limited access dataset and meta-analysis
Peer reviewedPublisher PD
Lithiation of silicon via lithium Zintl-defect complexes
An extensive search for low-energy lithium defects in crystalline silicon
using density-functional-theory methods and the ab initio random structure
searching (AIRSS) method shows that the four-lithium-atom substitutional point
defect is exceptionally stable. This defect consists of four lithium atoms with
strong ionic bonds to the four under-coordinated atoms of a silicon vacancy
defect, similar to the bonding of metal ions in Zintl phases. This complex is
stable over a range of silicon environments, indicating that it may aid
amorphization of crystalline silicon and form upon delithiation of the silicon
anode of a Li-ion rechargeable battery.Comment: 4 pages, 3 figure
Timeliness and content of retraction notices for publications by a single research group
Funding The study received no specific funding. MB is the recipient of an HRC Clinical Practitioner Fellowship. The Health Services Research Unit is funded by the Chief Scientist Office of the Scottish Government Health and Social Care Directorates. The authors are independent of the HRC. The HRC had no role in study design, the collection, analysis, and interpretation of data, the writing of the article, or the decision to submit it for publication.Peer reviewedPostprin
Should adults take vitamin D supplements to prevent disease?
Funding: Funded by the Health Research Council (HRC) of New Zealand. The authors are independent of the HRC. The HRC had no role in study design, the collection, analysis, and interpretation of data,Peer reviewe
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